Modern diesel engines often include subsystems designed to increase performance. One example of such a subsystem includes an engine brake. An engine brake can be used to slow a vehicle faster than service brakes and without significant component wear by, for example, opening the engine's exhaust valves during a compression stroke of the engine. Opening the exhaust valves releases kinetic energy transferred from the moving vehicle to the air in the engine's cylinders in the form of compression and heat, and minimizes the energy returned back to the vehicle. The amount of engine braking is dependent upon the amount of air available for compression in the cylinder. That is, a larger volume of air within the cylinder will require and, thus, dissipate more compression energy. Therefore an engine brake will provide more braking when more air is available.
Another example of a performance enhancing engine subsystem includes a particulate trap and associated regeneration device. Diesel engines exhaust a complex mixture of air pollutants composed of solid particulate material in the form of unburned carbon particles. In order to meet stringent emissions standards, engine manufacturers have developed devices for treatment of engine exhaust after it leaves the engine. One such exhaust treatment device is the particulate trap, which includes a filter designed to collect particulate matter from the exhaust flow of an engine. The use of the particulate trap for extended periods of time, however, enables particulate matter to accumulate on the filter, thereby causing damage to the filter and/or a decline in engine performance. One method of restoring the performance of a particulate trap includes regeneration. Regeneration of a particulate trap filter is accomplished by increasing the temperature of the filter and the trapped particulate matter above the combustion temperature of the particulate matter, thereby burning away the collected particulate matter. This increase in temperature may be accomplished by heating the exhaust gases upstream from the particulate trap with the use of a burner that creates a flame within the exhaust conduit leading to the particulate trap. The burner may include a fuel injector for creating the flame, and the burner may be supplied with air from the intake system of the engine.
As the number and complexity of engine subsystems increases, so does their interaction with and effect upon each other. For example, if air from the engine intake is supplied to the regeneration device to aid in combustion, then the effectiveness of engine braking may be reduced due to the reduced amount of air available for compression within the cylinders. Each engine subsystem and its related control can be designed to either isolate effects upon other subsystems, or to allow the subsystems to cooperate and positively effect each other.
One example of an engine having cooperating subsystems is described in U.S. Patent Application Publication no. 2005/0172617 (the '617 publication) by Persson, published on Aug. 11, 2005. The '617 publication discloses a method of regenerating a particulate filter by injecting fuel into an exhaust stream to raise the temperature of the exhaust. The injected fuel is oxidized by an oxidation catalyst upstream from particulate filters, thereby heating the exhaust and the particulate filter to a temperature sufficient to ignite carbon particles trapped in the particulate filter. Because the injected fuel, by itself, may be insufficient to ignite the trapped carbon particles, the regeneration system only operates during periods of engine braking, due to the increased exhaust temperatures that occur during engine braking. In this manner, heat from the injected fuel, combined with the elevated exhaust temperatures of engine braking, may be sufficient to regenerate the particulate filter.
While the system of the '617 publication may allow related subsystems to positively affect each other, it may be too limiting. Specifically, although the system may be capable of sufficiently regenerating a particulate filter, it is dependent upon the activation of engine braking. In instances where engine braking is not active or only active for a short time (i.e. a time insufficient to produce adequate temperatures), regeneration may be only minimally successful, thereby leading to reduced engine performance and economy, and an increased need for particulate filter service.
The system of the present disclosure solves one or more of the problems set forth above.